In semiconductor devices, with the increasing demand for higher performance, higher functionality, and lower power consumption, circuit patterns have been increasingly miniaturized. Accordingly, demand for removal of contaminant metals that would reduce the production yield has been significantly increased. Therefore, it is desirable that contaminant metals such as iron or zinc be not contained in a silylating agent liquid for forming a protective film for imparting hydrophobicity to a substrate (see, for example, Patent Document 1), a material for forming a fine membrane (see, for example, Patent Document 2), and a diffusing agent composition that is used for diffusing a dopant into a semiconductor substrate.
Such chemical solutions for use in the process of manufacturing semiconductor devices are cleaned beforehand to remove contaminant metals such as iron and zinc by way of a filter device or the like. The filter device usually includes a filter medium with a porous membrane.
Since impurities such as metal ions are removed, porous membranes capable of removing minute substances such as nanoparticles are desirable. Nylon, polyethylene, polypropylene, PTFE, and the like, are typically used as filter membranes capable of removing impurities from a chemical solution or a resin material to be used for a semiconductor device or the like. For example, it is known that organic impurities can also be removed by way of a filter membrane of nylon or the like (for example, see Patent Document 3).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-114414
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2005-171067
Patent Document 3: Japanese Patent No. 4637476